Means for measuring thickness of sheet material

ABSTRACT

A stationary thickness gauge is combined with a movable thickness gauge to measure the true thickness in the lateral direction of a running web or sheet material. The movable thickness gauge is moved in a direction transverse to the running direction of the web or sheet.

United States Patent Takenaka et al.

[ 51 June 6,1972

MEANS FOR IVIE'ASURING THICKNESS US. Cl 73/37.7, 26/70, 250/2l9 TH Int.Cl. ..G01b 13/06 Field of Search ..73/37.5-37.7, 159,

73/l50; 250/219 TH; 26/57 E, 70

DIFFERENCE CALCULATOR [56] References Cited UNITED STATES PATENTS3,179,800 4/1965 McNamera ...250/219 TH X 2,656,845 10/1953 Lindsay...250/2l9 TH X 3,185,024 5/1965 McCreanor ..250/2l9 TH X PrimaryExaminer-Louis R. Prince Assistant ExaminerWilliam A. Henry, llAtmrneySughrue, Rothwell, Mion, Zinn and Macpeak [57] ABSTRACT Astationary thickness gauge is combined with a movable thickness gauge tomeasure the true thickness in the lateral direction of a running web orsheet material. The movable thickness gauge, is moved in a directiontransverse to the running direction of the web or sheet.

6 Claims, 4 Drawing figures l5 2 S 5 AVERAGE MOVEABLE THICKNESSCALCULATOR GAGE DIFFERENCE CALCULATOR l7 lNDlCATOR I PATENTEDJUH 6 m2SHEET 10F 2 INVENTORS h HARUO TAKENAKA 2 HIROSHI OKUYAMA NOBURO msmoEHCHI om jgyL/M/ M/ ATTORNEYS PATENTED 5 I3 2 3,667, 283

SHEET 2 OF 2 I T2 T5 2 STATIONARY AVERAGE AVERAGE MOVEABLE THICKNESSTHICKNESS GAGE CALCULATOR CALCULATOR I GAGE T3 T4 5 T J I DIFFERENCEDIFFERENCE l CALCULATOR CALCULATOR DIFFERENCE 3 CALCULATOR INDICATOR 2COATING FIG. 4

MEANS FOR MEASURING THICKNESS OF SHEET MATERIAL BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention relates to'ameans for measuringthe true thickness of a running web or sheetmaterial, and'more specifically to a means for measuring the truethickness of 'a running web or sheet material in the lateral directionthereof.

2. Description of the Prior Art 7 In known conventional types ofthickness measuring means, movable thickness meters have been used formeasuring the thickness of a running web in the lateraldirectionthereof. The thickness meter is moved in a path transversely of (andrectangular to) the running direction of the web in such means. For sucha type of thickness measuring means employed in producing sheets, filmand the like, air-microgauge type thickness meters, strain gauge typethickness meters, supersonic type thickness meters, B-ray thicknessmeters and the like, have been used. Since the thicknessmeter asdescribed above is moved in a path transversely of the running directionof the web, the scanning locus of the thickness meter on the running webis a skewed line. According to the measured thickness along the skewedline on the web, a profile of thickness in the lateral direction isobtained.

In accordance with the obtained thickness profile in the lateraldirection of the web, the adjustable parameters of the producing machinemay be controlled to obtain a web of uniform thickness in the lateraldirection. For instance the temperature distribution in the lateraldirection, the clearance between the upper and lower rollers or thecross angle of the rollers may be controlled in order -to obtain auniform thickness.

However, the control of the web thickness according to the thicknessprofile obtained 'by the lateral movement of the thickness meter asdescribed above does not always result in a uniform thickness in thelateral direction.

In an actual sheet producing method utilizing an extruding screw typemachine, there is a variation in thickness in the .running direction ofthe sheet produced which is due, inter alia, to the variation in thespeed of rotation of the extruding screw, mechanical vibrations, theeccentricity of the quench from axis, the back lash of the driving gearor the slip of the driving belt.

Any variation in tension of the running web caused by any difference infriction coefficient in the peripheral direction of the surface of theperiphery of the idle roller causes avan'ation in thickness in therunning direction of the web produced.

In addition to the above-described variation in thickness of the web inthe running direction thereof, there is a variation in thickness of theweb in a direction transverse to the running direction thereof. Thevariation in thickness in the lateral direction (i.e., a directionrectangular to the running direction) does not occur without positivelyvarying the thickness in the lateral direction with some controllingmeans. Therefore, if there is no variation in thickness in the runningdirection of the web, the proper regulation of thickness can be achievedby controlling the thickness controlling means in accordance with thethickness profile obtained by performing the thickness measurement witha thickness meter scanning only in the lateral direction. However, sincethere is a variation in thickness in the runningdirection, it isimpossible to properly control the thickness of the web by onlyoperating the thickness controlling means in accordance with thethickness profile obtained by performing the thickness measurement witha thickness meter scanning the web only in the lateral direction. Thisoccurs because the scanning meter is actually scanning the web skewlywith respect to the running direction of the web, since the meter isbeing moved in a direction transversely of the running direction of theweb.

A manner of resolving the above-described problem is to move thethickness meter diagonally with respect to the running direction of theweb so that the component of the speed of scanning in the runningdirection. is equal, to, the speed of running of the web. By.moving thethickness meter as. described above,,the thickness meter is moved as aresult relatively in the lateral direction of the web. Thus, thethickness of the web in the lateral direction is measured and thecorrect thickness profile is obtained. Inaccordance withthe thicknessprofile thus obtained, the proper thickness controlling procedures canbe chosen. However-,the scanning speed of the thickness meter isgenerallyv limited by the response time of the thickness meter, noiseand the like. Since the runningspeed of the web is comparatively largewith respect to the possible speed of the scanning meter, the thicknessmeter is to be scanned in. a direction inclined: at a small angle to therunning direction of theweb. Accordingly, the path of the scanningthickness meter should be; remarkably, large. Therefore, a large spaceis required to carry out the above-described method. In some cases, itis impossible to carry out the abovedescribed method of resolution.

Considering the drawbacks of the above-described conventional method ofmeasuring the thicknessof a running web, a new method of measuring thethickness of a moving web has long been sought after.

SUMIVIARY OF THE INVENTION The present invention provides a means formeasuring the thickness of a moving sheet material comprising astationary thickness. meter for measuring the thickness of a running webalong the running direction thereof and a movable thickness metermovable in a direction transversely tothe running direction of the web.The stationary thickness meter measures the thickness of the web in therunning direction and the movable thickness meter measures the thicknessof the running web in the skewed direction.

Accordingly, by compensating the measured thickness of the web in theskew direction in accordance with the measured thickness of the web inthe running direction, the true thickness profile along the lateraldirection of the web can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of the means formeasuring the thickness of a moving sheet material in accordance withthe present invention; and 1 FIG. 2 is a diagram showing the principleof the method of measuring the thickness .of the running web inaccordance with the present invention;

FIG. 3 is a block diagram showing the apparatus for calculating thethickness of the moving sheetof material in accordance with the presentinvention; and

FIG. 4 is a diagram showing the apparatus for measuring the thickness ofa coating on a sheet of moving material in accordance with the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1,reference numeral 1 indicates a stationary thickness meter, 2 indicatesa movable thickness meter, and 3 indicates a running web which moves ina direction from left to right in the drawing. The movable thicknessmeter 2 moves in a direction rectangular to the running direction, i.e.,in the lateral direction of the web 3. The locus of the movablethickness meter 2 on the running web3isshown by the skew line 4.

Referring to FIG. 2, 5 indicates a profile of the web thickness alongthe running direction of the web 3 obtained by moves on the running web3. That is, the points 0, ,11 g Ii, are the points where the thicknessof the web 3 is measured and the profile of thickness 7 is obtained byprojecting the measured thickness at the measuring points on line 9 ontothe lateral line'8.

The numeral 10 indicates the running web moving in the direction shownby the arrow. The numeral 11 indicates a profile of the thickness drawnby the method of the present invention. This profile 11 shows the truethickness profile along the lateral direction of the web. According tothe drawn thickness 11 of the present invention, the thickness along thelateral direction of the web can be controlled so as to be con stant,and thus a uniform thickness can be obtained.

The manner of forming the correct profile ll of the web thickness inaccordance with the present invention will now be described in detail.

The thickness profile 11 is obtained by substracting the thicknessprofile 5 along .the' running direction of the web measured by thestationary thickness meter 1 from the thickness profile 7 along the skewline 4 onthe web measured by the movable thickness meter 2. That is,since the thickness at the measuring points 0,, b,, d,, f,, h, on theprofile 5 to be subtracted from the profile 7 is zero, the true profileof the thickness obtained has a thickness equal to the measuredthickness on the profile 7 along the skew line 4, measured by thethickness meter 2; 0; b d ;f h

At the measuring points a and e, since the thickness along the runningdirection shown by the profile 5 is smaller than the average, a, and q,the true thickness obtained by subtracting the profile 5 from theprofile 7 becomes larger than profile 7.

Thus, a thickness larger than the measured thickness is obtained asindicated by a; and e 'on the profile 11. At the measuring points c and3, since the thickness along the running direction shown by the profile5 is larger than the average as shown at c, and 3 the true thicknessobtained by subtracting the profile 5 from the profile -7 becomessmaller than the profile 7. Thus, a thickness smaller than the measuredthickness is obtained at the points a and 3 The profilell of thethickness thus obtained provides the true thickness along the lateraldirection of the web.

Of course, the assumption that the thickness profile 11 thus obtainedprovides the true thickness along the 'lateral direction of the webisbased on'the experimental results that the thickness variation alongthe running direction of the web is equally measured at each point alongthe lateral line of the web l v FIG. 3 is a block diagram showing theapparatus for calculating the true thickness of a moving sheet ofmaterial. The

output of stationary thickness gauge 1 is applied to average calculator12' which calculates the average value of the thickness of the materialalong the longitudinal direction of the material. The output of averagecalculator 12 corresponds to line 6 which is the average of profile 5 inFIG. 2. The output of average calculator 12 is applied to differencecalculator 13 along with the output of the stationary thickness gauge 1.Difference calculator l3 calculates the difference between profile 5 andaverage 6 shown in FIG. 2. The output of movable thickness gauge 2 isapplied to average calculator 15 which thickness measured bythestationary'thickness meter 1 with' the thickness measured by themovable thickness meter, meacalculates the average value of thethickness of the material as measured by movable thickness gauge 2. Thiscorresponds to line 8 in FIG. 2 which is the average valueof profile 7.The output of the average calculator l5 and the output of movablethickness gauge 2 are applied to difference calculator 14 whichcalculates the difi'erence between average value 8 and profile 7-in FIG.2. The output of difference calculators l3 and 14 are applied to adifference calculator 16 which calculates the difference between thesetwo outputs. The output of difference calculator 16 corresponds toprofile 1 1 shown in FIG. 2. The output of difference calculator 16,which is profile 11, may be applied to a suitable indicator 17.

- More preferably, the true thickness of the running web along thelateral direction thereof can be measured as follows. If the two pointson one lateral line of the running web are measured and the thicknessesthereof are compared, the thickness profile along the lateral directionof the web can be obtained by continuously measuring the two points atvarious positions. Since the stationary thickness meter 1 measuring thethickness of the web 3 along the longitudinal direction thereof isspaced apart from the movable thickness meter 2 in the running directionof the web by the distance 1, a means for memorizing the measuredthickness for some time is required. Since the web 3 is running at aconstant speed v from the stationary thickness meter side of the movablethickness meter side, the time for the web 3 to travel from thestationary thickness meter 1 to the movable thickness meter 2is I/v.Therefore, it is possible to compare the two points on one lateral lineof the web 3 and to get the true thickness profile along the lateraldirection if the measured thickness of the web measured by thestationary thickness meter is memorized and reproduced after the timeI/v.

The thickness measured by the stationary thickness meter 1 is memorizedby a magnetic recording system and reproduced after the above-describedtime. By comparing the reproduced suring the thickness at the point onthe lateral line on which the point where the thickness was measured bythe stationary thickness meter exists, the true thickness profile in thelateral direction can be obtained. By continuously making theabovedescribed operation (comparing the thickness measured by thestationary thickness meter with the thickness measured by the movablethickness meter moved along a direction rectangular to the runningdirection of the web) the correct thickness profile representing thethickness along the lateral direction of the web can be obtained even ifthe thickness varies in a direction along the running direction of theweb.

In order to reproduce the measured thickness afier the prescribed time,e. g., l/v, and in order to subtract the thickness measured by thestationary thickness meter 1 from the thickness measured by the movablethickness meter 2 as shown in FIG. 1, various conventionally known typesof electrical methods can be employed. For instance, the thicknessprofile is converted into the magnitude in voltage an analog value andthe analog value is in turn converted into a digital value such as afrequency so as to be memorized in a magnetic tape, magnetic disc,magnetic drum, and the like, and to be reproduced after the time l/v.Then the reproduced digital value is reversely converted into thevoltage and the voltage operates a proper electric circuit for operationof the mechanism.

It is apparent that the thickness'measuring means in accordance with thepresent invention is duly operated even if the positions of thestationary thickness meter and the movable thickness meter are reversed..Even if the variation in thickness of the web in the running directionis small and the gradient of thickness variation is small enough, it ispossible to operate the true thickness of the web in the lateraldirection without using any recording means for memorizing the measuredthickness by disposing the two thickness meters in close relationship.That is, by making the above-described distance I as small as possible,there becomes no need to memorize and reproduce the measured thickness.

The preset invention is also applicable to measure the thickness profilein the lateral direction of a coated layer. In coating a sheet with acoating layer while continuously feeding thesheet, it is very difficultto maintain the' thickness of the coating layer uniform in thelateraldirection as well as in the longitudinal direction. In such a case,bydisposing the stationary thickness meter on the uncoated sheetmaterial and disposing the movable thickness meter above the coatedsheet material, it is possible to measure the thickness of the uncoatedsheet material and the coated sheet material separately. It is possible,accordingly, to obtain the thickness profile of the coated layer in thelateral direction by operating the difference in thickness between theuncoated sheet thickness and the coated sheet thickness.

FIG. 4 illustrates the manner in which the present invention may be usedto measure the thickness profile in the lateral direction of a coatedlayer. Stationary thickness gauge 1 is positioned over an uncoatedportion of movable material 3. As the material passes coating applicator18 a coating 19 is applied to the upper surface of material 3. Themovable thickness gauge 2 is positioned above the coated portion ofmovable material 3. In this manner it is possible to obtain thethickness profile of the coated layer in the lateral direction byconnecting stationary thickness gauge 1 and movable thickness gauge 2into the circuit shown in FIG. 3.

What is claimed is:

1. Apparatus for measuring the thickness of an advancing continuoussheet material comprising:

a. stationary thickness gauge means for measuring the thickness of saidsheet as said sheet advances past said stationary thickness gauge meansin the longitudinal direction;

. first calculating means, coupled to the output of said stationarythickness gauge means, for calculating the average value of the outputof said stationary thickness gauge means;

c. second calculating means, coupled to the output of said stationarythickness gauge means and the first calculating means, forcalculatingthe difference between the outputs of the stationarythickness gauge means and the first calculating means;

d. movable thickness gauge means adapted to move in a directiontransverse to the direction of movement of the advancing sheet formeasuring the thickness of said advancing sheet;

e. third calculating means, coupled tothe output of said movablethickness gauge means, for calculating the average value of the outputof the movable thickness gauge means;

I. fourth calculating means, coupled to the output of said movablethickness gauge means and said third calculating means, for calculatingthe difference between the outputs of the movable thickness gauge meansand the third calculating means; and

g. fifth calculating means, coupled to the output of said secondcalculating means and said fourth calculating means, for calculating thedifference between the outputs of the second calculating means and thefourth calculating means whereby the output of the fifth calculatingmeans is equal to the true thickness of said continuous sheet.

2. Apparatus for measuring the thickness of a sheet material as definedin claim 1, wherein said stationary thickness gauge means is separatedfrom said movable thickness gauge means in the longitudinal direction ofsaid advancing sheet material, and wherein said apparatus furtherincludes a means for memorizing a first measured thickness andreproducing said first measured thickness after a predetermined time sothat said first measured thickness may be compared with a secondmeasured thickness at a point on the same lateral line of said advancingsheet material as that at which said first measured thickness wasmeasured.

3. Apparatus for measuring the thickness of a sheet material as definedin claim 1, wherein said stationary thickness gauge means is disposed inclose relationship with said movable thickness gauge. means.

4. Apparatus for measuring the thickness of a sheet material as definedin claim 1 further including coating means for applying a coating layerto said sheet material wherein said stationary thickness gauge meansmeasures the thickness of said material prior to the application of saidcoating and said movable thickness gauge means measures the combinedthickness of said material and said coating whereby said apparatusmeasures the true thickness of said coating.

5. A method for measuring the thickness of an advancing continuous sheetmaterial comprisingthe stepspf:

a.-measunng the thickness of sat sheet with a stationary thickness gaugemeans as said sheet advances past said stationary thickness gauge meansin the longitudinal direction;

b. calculating the average value of the output of said stationarythickness gauge means;

c. calculating a first difi'erence equal to the difference between theoutput of said stationary thickness gauge means and the calculatedaverage of the output of the stationary thickness gauge means;

measuring the thickness of said advancing sheet with a movable thicknessgauge means adapted to move in a direction transverse to the directionof movement of the advancing sheet;

e. calculating the average value of the output of said movable thicknessgauge means;

f. calculating a second difference equal to the difference between theoutput of the movable thickness gauge means and the calculated averageof the output of the movable thickness gauge means; and calculating athird difference equal to the difference between said first differenceand said second difference whereby said third difference is equal to thetrue thickness of said continuous sheet.

6. Apparatus for measuring the thickness of a coated layer comprising astationary thickness gauge means disposed on an uncoated portion of acontinuous advancing sheet material, and a movable thickness gauge meansdisposed on a coated portion of said sheet material calculating meanscoupled to said stationary thickness gauge means and said movablethickness gauge means for calculating the true thickness of said sheetmaterial with said coated layer.

* II i It

1. Apparatus for measuring the thickness of an advancing continuoussheet material comprising: a. stationary thickness gauge means formeasuring the thickness of said sheet as said sheet advances past saidstationary thickness gauge means in the longitudinal direction; b. firstcalculating means, coupled to the output of said stationary thicknessgauge means, for calculating the average value of the output of saidstationary thickness gauge means; c. second calculating means, coupledto the output of said stationary thickness gauge means and the firstcalculating means, for calculating the difference between the outputs ofthe stationary thickness gauge means and the first calculating means; d.movable thickness gauge means adapted to move in a direction transverseto the direction of movement of the advancing sheet for measuring thethickness of said advancing sheet; e. third calculating means, coupledto the output of said movable thickness gauge means, for calculating theaverage value of the output of the movable thickness gauge means; f.fourth calculating means, coupled to the output of said movablethickness gauge means and said third calculating means, for calculatingthe difference between the outputs of the movable thickness gauge meansand the third calculating means; and g. fifth calculating means, coupledto the output of said second calculating means and said fourthcalculating means, for calculating the difference between the outputs ofthe second calculating means and the fourth calculating means wherebythe output of the fifth calculating means is equal to the true thicknessof said continuous sheet.
 2. ApparatUs for measuring the thickness of asheet material as defined in claim 1, wherein said stationary thicknessgauge means is separated from said movable thickness gauge means in thelongitudinal direction of said advancing sheet material, and whereinsaid apparatus further includes a means for memorizing a first measuredthickness and reproducing said first measured thickness after apredetermined time so that said first measured thickness may be comparedwith a second measured thickness at a point on the same lateral line ofsaid advancing sheet material as that at which said first measuredthickness was measured.
 3. Apparatus for measuring the thickness of asheet material as defined in claim 1, wherein said stationary thicknessgauge means is disposed in close relationship with said movablethickness gauge means.
 4. Apparatus for measuring the thickness of asheet material as defined in claim 1 further including coating means forapplying a coating layer to said sheet material wherein said stationarythickness gauge means measures the thickness of said material prior tothe application of said coating and said movable thickness gauge meansmeasures the combined thickness of said material and said coatingwhereby said apparatus measures the true thickness of said coating.
 5. Amethod for measuring the thickness of an advancing continuous sheetmaterial comprising the steps of: a. measuring the thickness of saidsheet with a stationary thickness gauge means as said sheet advancespast said stationary thickness gauge means in the longitudinaldirection; b. calculating the average value of the output of saidstationary thickness gauge means; c. calculating a first differenceequal to the difference between the output of said stationary thicknessgauge means and the calculated average of the output of the stationarythickness gauge means; d. measuring the thickness of said advancingsheet with a movable thickness gauge means adapted to move in adirection transverse to the direction of movement of the advancingsheet; e. calculating the average value of the output of said movablethickness gauge means; f. calculating a second difference equal to thedifference between the output of the movable thickness gauge means andthe calculated average of the output of the movable thickness gaugemeans; and g calculating a third difference equal to the differencebetween said first difference and said second difference whereby saidthird difference is equal to the true thickness of said continuoussheet.
 6. Apparatus for measuring the thickness of a coated layercomprising a stationary thickness gauge means disposed on an uncoatedportion of a continuous advancing sheet material, and a movablethickness gauge means disposed on a coated portion of said sheetmaterial calculating means coupled to said stationary thickness gaugemeans and said movable thickness gauge means for calculating the truethickness of said sheet material with said coated layer.